1. Field of the Invention
The present invention relates to a drive apparatus which is used as a drive source for opening/closing a window mounted on the roof and door of an automobile, as a drive source for opening/closing the door of the automobile and as a drive source required to open/close an operation member mounted in and on the house, building, machine equipment or the like.
2. Description of the Related Art
A drive apparatus for opening/closing a glass window connected to a power transmission cable by moving that cable in an axial direction is known in the art. This type of cable is obtained by spirally winding a wire on the outer periphery of a wire rope (core wire) so that the spiral wire provides a spiral rib as a spiral tooth-like projection. The cable is inserted through a metal guide pipe and moved in that state. The cable is moved in an axial direction by a motor or by manually rotating a handle.
The cable is flexible in nature and is freely handled, thus offering the advantage of arranging an associated motor and handle with a proper latitude. For this reason, the guide pipe may have a curved portion.
In the conventional guide pipe having such a curved portion, however, when the glass window as a load is to be moved, a portion of the cable is slidably moved, while being tightly engaged with the inner surface of the curved portion of the pipe. A larger frictional resistance occurs at the curved portion of the cable, failing to effectively transmit a propulsive force from the motor or handle to the load.
With the curvature radius of the curved portion of the cable set to be small, than a greater frictional resistance is unfavorably increased at the curved portion of the cable. For this reason, it is difficult to make the drive apparatus compact.
Further, since the guide pipe is made of a metal as set out above, a noise is liable to be produced at the curved portion of the cable during the slide movement of the cable.
Suppose that the conventional drive apparatus is used to open/close the glass window in a down/up motion. In this case, the weight of the window glass affects the speed with which the glass window is moved. That is, the different speed is involved between moving the window in the upward direction and moving the window in the downward direction.